The 4th probably made some deal with that death god to take his life but seal the soul of the kyubi in Naruto instead, and to answer your poll id say Naruto, the 4th probably had insight into how he would develop and you know how all of Konoha was suprised that Naruto could handle the kyubi chakra without losing himself, thats probably hinting at the reason the 4th sealed it in Naruto